1. Field of the Invention
The present invention relates to a recording apparatus and a recording method for performing light modulation recording, that is, data recording on a recording medium by a laser beam modulated by recording data.
2. Description of the Related Art
When performing light modulation recording on a recording medium such as an optical disk or the like, a laser emits light in pulses in order to perform thermal control for shaping a pit (mark) to be formed on the disk.
Specifically, a pulse waveform as a driving pulse for driving the laser is arranged, and the level (peak value) during each pulse period is controlled, thereby controlling the laser power and the laser irradiation time.
For example, data is written on disk media in which data can be written, namely, CD-recordable (CD-R) which is CD-write once (CD-WO) and CD-rewritable (CD-RW), at data writing speeds of ×1, ×2, and ×4 speeds. Laser emission control in accordance with the writing speed is performed as shown in FIGS. 14 and 15. The ×1 speed corresponds to 1.2 to 1.4 m/s, which is achieved by rotating a disk in a constant linear velocity (CLV) mode.
FIG. 14 shows a driving pulse generated when writing at a ×1 writing speed or a ×2 writing speed.
It is known that a CD system generates an EFM signal as recording data. The pulse duration of the EFM signal is specified within a range of 3 T to 11 T, as shown in FIG. 14. The letter “T” corresponds to one channel clock period.
Based on the EFM signal, an equalized EFM signal (hereinafter referred to as an “EQEFM signal”) is generated, as shown in FIG. 14. The EQEFM signal is used as a laser driving pulse.
In the example shown in FIG. 14, the EQEFM signal has a pulse which basically has a duration of (N−1)T compared with (N)T of the EFM pulse (in the drawing, θ=1 T).
For example, concerning the EFM signal having a pulse duration of 4 T, the EQEFM signal having a pulse duration of 3 T is generated. Concerning the EFM signal having a pulse duration of 11 T, the EQEFM signal having a pulse duration of 10 T is generated. With regard to the EFM signal having a pulse duration of 3 T, a period of α=0.13 T is added to the pulse duration of the EQEFM signal. The symbol “Pw” represents the writing laser power.
The EQEFM signal corresponds to the laser emission level. Concerning the EFM pulse having a duration of (N)T, the EQEFM signal having a pulse duration of (N−1)T is generated. This is configured so in anticipation of a portion in which a pit is formed by thermal accumulation immediately after the laser emission is stopped.
Therefore, the relationship between the EFM signal and the formed pits P and lands L is such that the pulse duration is associated with the pit length and the land length, as shown in FIG. 16.
FIG. 15 shows a driving pulse generated when writing at a ×4 writing speed.
In the example shown in FIG. 15, the EQEFM signal has a pulse which basically has a duration of (N−0.5)T with respect to the EFM pulse having a duration of (N)T (in the drawing, θ=0.5 T). For example, concerning the EFM signal with a pulse duration of 4 T, the EQEFM signal having a pulse duration of 3.5 T is generated.
In this case, an increased power portion expressed by ΔP is added to period ODT at the leading edge of the pulse. Hereinafter, the increased power portion or a pulse for forming the increased power portion is referred to as an overdrive pulse.
FIG. 17 shows pits and lands formed by a laser which is driven to emit light based on a driving pulse generated by the method shown in FIG. 14. FIG. 18 shows pits and lands formed by a laser which is driven to emit light based on a driving pulse generated by the method shown in FIG. 15.
FIGS. 17 and 18 show the laser power controlled by driving pulses generated based on the EFM signal shown in FIG. 16. The symbol “Pw” represents the writing laser power, and the symbol “Pr” represents the reading laser power. FIG. 17 and 18 show the formed pits P and lands L.
Referring to FIGS. 17 and 18, period A and period B each indicate a delay from the start of the laser beam emission until the formation of the pit P starts. Period a and period b each indicate a delay from the termination of the laser emission until the formation of the pit P is completed.
Recently, recording rates have been increased. Concerning CD-R and CD-RW, the recording rates have been further increased. For example, recording at a ×8 speed has been achieved.
Upon recording at the ×8 speed, when the laser power is controlled by the method shown in FIG. 14 or by the method shown in FIG. 15, intersymbol interference occurs, and jitter of the recording data increases. In the worst case, the recording data cannot be read.